From 309c0866fa8dc7793846e607015cc627dcd98350 Mon Sep 17 00:00:00 2001
From: Christoph Klaffl <christoph@phreaker.eu>
Date: Mon, 7 Dec 2020 22:40:28 +0100
Subject: [PATCH] implemented removal of conflicting snapshots with
 force-delete option

---
 README.md                                    |  4 +-
 syncoid                                      | 32 ++++++++++++-
 tests/syncoid/8_force_delete_snapshot/run.sh | 48 ++++++++++++++++++++
 3 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100755 tests/syncoid/8_force_delete_snapshot/run.sh

diff --git a/README.md b/README.md
index b4558c0..5a052e9 100644
--- a/README.md
+++ b/README.md
@@ -336,11 +336,11 @@ As of 1.4.18, syncoid also automatically supports and enables resume of interrup
 
 + --force-delete
 
-	Remove target datasets recursively (WARNING: this will also affect child datasets with matching snapshots/bookmarks), if there are no matching snapshots/bookmarks.
+	Remove target datasets recursively (WARNING: this will also affect child datasets with matching snapshots/bookmarks), if there are no matching snapshots/bookmarks. Also removes conflicting snapshots if the replication would fail because of a snapshot which has the same name between source and target but different contents.
 
 + --no-clone-handling
 
-	This argument tells syncoid to not recreate clones on the targe on initial sync and doing a normal replication instead.
+	This argument tells syncoid to not recreate clones on the target on initial sync and doing a normal replication instead.
 
 + --dumpsnaps
 
diff --git a/syncoid b/syncoid
index b771d8f..7d8329b 100755
--- a/syncoid
+++ b/syncoid
@@ -813,6 +813,36 @@ sub syncdataset {
 							if ($exitcode < 2) { $exitcode = 2; }
 							return 0;
 						}
+					} elsif ($args{'force-delete'} && $stdout =~ /\Qdestination already exists\E/) {
+						(my $existing) = $stdout =~ m/^cannot restore to ([^:]*): destination already exists$/g;
+						if ($existing eq "") {
+							warn "CRITICAL ERROR: $synccmd failed: $?";
+							if ($exitcode < 2) { $exitcode = 2; }
+							return 0;
+						}
+
+						if (!$quiet) { print "WARN: removing existing destination: $existing\n"; }
+						my $rcommand = '';
+						my $mysudocmd = '';
+						my $existingescaped = escapeshellparam($existing);
+
+						if ($targethost ne '') { $rcommand = "$sshcmd $targethost"; }
+						if (!$targetisroot) { $mysudocmd = $sudocmd; }
+
+						my $prunecmd = "$mysudocmd $zfscmd destroy $existingescaped; ";
+						if ($targethost ne '') {
+							$prunecmd = escapeshellparam($prunecmd);
+						}
+
+						my $ret = system("$rcommand $prunecmd");
+						if ($ret != 0) {
+							warn "CRITICAL ERROR: $rcommand $prunecmd failed: $?";
+							if ($exitcode < 2) { $exitcode = 2; }
+							return 0;
+						} else {
+							# redo sync and skip snapshot creation (already taken)
+							return syncdataset($sourcehost, $sourcefs, $targethost, $targetfs, undef, 1);
+						}
 					} else {
 						warn "CRITICAL ERROR: $synccmd failed: $?";
 						if ($exitcode < 2) { $exitcode = 2; }
@@ -1994,4 +2024,4 @@ Options:
   --no-clone-handling   Don't try to recreate clones on target
   --no-privilege-elevation  Bypass the root check, for use with ZFS permission delegation
 
-  --force-delete        Remove target datasets recursively, if there are no matching snapshots/bookmarks
+  --force-delete        Remove target datasets recursively, if there are no matching snapshots/bookmarks (also overwrites conflicting named snapshots)
diff --git a/tests/syncoid/8_force_delete_snapshot/run.sh b/tests/syncoid/8_force_delete_snapshot/run.sh
new file mode 100755
index 0000000..899092a
--- /dev/null
+++ b/tests/syncoid/8_force_delete_snapshot/run.sh
@@ -0,0 +1,48 @@
+#!/bin/bash
+
+# test replication with deletion of conflicting snapshot on target
+
+set -x
+set -e
+
+. ../../common/lib.sh
+
+POOL_IMAGE="/tmp/syncoid-test-8.zpool"
+POOL_SIZE="200M"
+POOL_NAME="syncoid-test-8"
+TARGET_CHECKSUM="ee439200c9fa54fc33ce301ef64d4240a6c5587766bfeb651c5cf358e11ec89d  -"
+
+truncate -s "${POOL_SIZE}" "${POOL_IMAGE}"
+
+zpool create -m none -f "${POOL_NAME}" "${POOL_IMAGE}"
+
+function cleanUp {
+  zpool export "${POOL_NAME}"
+}
+
+# export pool in any case
+trap cleanUp EXIT
+
+zfs create "${POOL_NAME}"/src
+zfs snapshot "${POOL_NAME}"/src@duplicate
+
+# initial replication
+../../../syncoid -r --debug --compress=none "${POOL_NAME}"/src "${POOL_NAME}"/dst
+# recreate snapshot with the same name on src
+zfs destroy "${POOL_NAME}"/src@duplicate
+zfs snapshot "${POOL_NAME}"/src@duplicate
+sleep 1
+../../../syncoid -r --force-delete --debug --compress=none "${POOL_NAME}"/src "${POOL_NAME}"/dst || exit 1
+
+# verify
+output1=$(zfs list -t snapshot -r -H -o guid,name "${POOL_NAME}"/src | sed 's/@syncoid_.*$'/@syncoid_/)
+checksum1=$(echo "${output1}" | shasum -a 256)
+
+output2=$(zfs list -t snapshot -r -H -o guid,name "${POOL_NAME}"/dst | sed 's/@syncoid_.*$'/@syncoid_/ | sed 's/dst/src/')
+checksum2=$(echo "${output2}" | shasum -a 256)
+
+if [ "${checksum1}" != "${checksum2}" ]; then
+	exit 1
+fi
+
+exit 0